Humidity responsive dryer control



Sept. 14, 1965 H. w. DEATON HUMIDITY RESPONSIVE DRYER CONTROL 2Sheets-Sheet 1 Filed Feb. 23 1962 INVENTOR. Home) dd Dea f0)? 2 m H15ATTORNEY United States Patent 3,205,590 HUMlDITY RESPQNSVE DRYER CONTROLHomer W. Deaton, Dayton, ()hio, assignor to General Motors Corporation,Detroit, Mich, a corporation of Delaware Filed Feb. 23, 1962, Ser. No.175,071 8 Claims. (Cl. 34-45) This invention relates generally to animproved power termination control circuit and more particularly to apoint relative humidity.

In the clothes drying art, it has been recognized that different fabricloads (size and type) have different drying characteristics whenconsidering dryer exhaust air humidity versus time for drying.Therefore, any device which automatically terminates a drying cycle onexhaust humidity alone cannot produce consistent drying results when theload varies both as to size and character of fabric. Note has been takenof the fact that the relative humidity of the outlet or exhaust airdrops as the temperature thereof rises. Using this fact, this inventionis directed to a control circuit which progressively lowers the humiditycontrol point at which the drying cycle will terminate. Thus, thisinvention recognizes that smaller loads and lighter fabrics are properlydry at lower exhaust air relative humidity readings.

Accordingly, it is an object of this invention to provide a dryertermination control circuit equally effective in terminating the dryingcycle of small or large loads of different fabrics.

Another object of this invention is the provision of a dryer terminationcontrol which is effective to select the control termination point inaccordance with the type of load being dried.

A more specific object of this invention is the provision of a humidityelement controlled dryer termination control in which the relativehumidity termination point is continuously reduced whenever the sensibletemperature of the dryer exhaust exceeds a predetermined value toindicate the load is approaching a dry condition.

Another object of this invention is the provision of an amplifier for adryer control for terminating the drying cycle, said amplifier beingactuated by a voltage divider circuit including a humidity sensingelement responsive to the dryer exhaust air and a variable resistanceelement which is continuously mechanically increased to lower therelative humidity control point at which the exhaust air at the sensingelement would be effective to terminate the drying cycle.

Another object of this invention is the provision of an improvedamplifier in a dryer control which includes relay coil winding inparallel with a transistor-the transistor being selectively operated bya voltage divider circuit having a humidity sensing element and avariable resistance.

A more general object of this invention is the provision of a relaycontrol circuit having a relay coil winding in parallel with atransistor or semiconductor switch means.

Another object of this invention is the provision of a. control for apower supply including a circuit having a relay coil actuatable forconnecting and disconnecting the circuit from said power supply, atransistor in parallel with said coil and a voltage divider circuit inparallel with said coil and connected to said transistor for biasingsaid transistor to actuate said coil.

Another object of this invention is provision of a voltage dividercircuit in a clothes dryer control, said voltage divider circuitincluding a variable resistance which is progressively increasedthroughout the drying cycle to change the point at which the dryingcycle is terminated.

Further objects and advantages of the present inven- Patented Sept. 14,1965 "ice tion will be apparent from the following description,reference being had to the accompanying drawings wherein preferredembodiments of the present invention are clearly shown.

in the drawings:

FIGURE 1 is a cross-sectional view of a clothes dryer suitable for usewith this invention;

FIGURE 2 is a schematic wiring diagram of the control circuit of thisinvention; and

FIGURE 3 is a graph of relative humidity versus time for the last partof a clothes drying cycle controlled in accordance with the teachings ofthis invention.

In accordance with this invention and with reference to FIGURE 1, aclothes dryer 10 is illustrated. The dryor includes a front wall 12, arear wall 14 and a top panel 16 having a control console 18 at the rearthereof. The walls 12, 14 and 16 partially form a casing for enclosing atumbling drum 20 which is journaled in a bearing 22 carried by a rearbulkhead 24. The tumbling drum 20 has a perforated rear wall 26 and aflanged collar 28 which surrounds an inwardly directed collar 30 on afront port plate 32. The front port plate 32 is fixed to a recessedshoulder 34 in the front wall 12 of the dryer cabinet. Thus, the portplate 32 and its integral collar 30 form the access passage for placingclothes within the tumbling drum 20.

A door 36 is hingedly mounted on the front wall of the dryer and carriesa lint collecting housing 38 which nests within the port plate 32 insealing engagement thereto when the door is closed. The lint collectinghousing carries a lint collecting screen 40 which is interposed betweenthe perforations -42 of the lint collector housing 38 on one side of thescreen 40 and an outlet passage 44 on the other side of the housing. Theport plate 32 carries an arcuate series of ports 46 at its lower edgewhich directs air into a front duct 48 leading to a blower 50 within thedryer cabinet. This blower 50 exhausts the air to the atmosphere througha duct 74. Between the front duct 48 and the blower 50 is a controlconduit 52 in which a humidity sensing element or sensor 54 resides. Anamplifier 56 in the dryer console is electrically connected to thesensor 54 and adapted to signal the end of the automatic drying cycle. Aheater 60 is included in the annular space between the bulkhead 24 andthe perforated rear wall 26 of the tumbling drum. A motor 62 ispositioned in the lower part of the dryer casing and adapted to drivethe blower 50 and rotate the tumbling drum 20 through a conventionalpulley and belt arrangement 64.

Air flow through the tumbling drum 20 for drying the clothes is thusafforded as follows. Air enters the back wall 14 of the dryer casingthrough openings, such as 66 and 68. The air is drawn through theperforations 70 of the rear bulkhead 24 and across the heating element60 into the tumbling drum 20. Air leaving the tumbling drum aftervaporizing moisture from the clothes enters the lint collecting housing38 through the perforations 42 thereof and has the lint filteredtherefrom by the screen 40. This exhaust air flowing from the tumblingdrum by way of the front duct 48 and the conduit 52 passes the humiditysensing element 54 prior to its being exhausted through the outlet duct74 to the atmosphere. This invention is directed to a control forterminating the drying cycle in the dryer describer hereinabove.

The control circuit is best seen in FIGURE 2 and includes apush-actuated start button 76 in an accessible location such as on thecontrol console of the dryer. The start button '76 is depressedmomentarily to energize a holding circuit which includes a holding relaycoil 78 and a switch 80 actuated by the holding coil. A delay means maybe provided for the push button 76 to prevent 3 its opening beforemoisture is reflected at the sensing element 54 in the dryer exhaust. Itshould be recognized, however, that .a more sensitive sensing element 54will preclude the necessity for this time delay in the start switch.

The dryer termination control includes an improved amplifier 56 having adirect current relay coil or winding 82 for actuating a switch 84 inseries with the holding circuit coil 78. The switch 84 is norm-ally openand is closable so long as the relay coil 82 is energized. By-passingthe relay coil 82 is a transistor 86 having its emitter 88 connected toone side of the coil 82, and its collector 90 connected to the otherside of the relay coil. Since the relay coil 82 is actuatable by directcurrent, a diode 92 is included in parallel relationship with the coilto pass current in one direction only. A capacitor 94 may also beincluded for relays which have a tendency to hum when used on AC. orpulsating D.C. A resistance 96, in series with the relay coil 82, mustbe small enough to permit the energization of the coil 82 with theavailable power supply. Grouping the foregoing components, the onlyelectrical connections to the amplifier 56 are a conductor 98 to oneside of the domestic 115 v.230 v. power supply line L and a conductor100 to the neutral side of the line N. The base connection 102 for thetransistor 86 extends out of the amplifier 56 and is connected to avoltage divide-r circuit which includes the humidity sensing element 54and a motorized resistance unit 104 in juxtaposition to the amplifier inthe console. The unit 104 ha a variable resistance 108 and a positioningmotor 106 which is thermally responsively energizable for progressivelyincreasing the resistance 108. Since the resistance 108 is gradually andprogressively increased during the drying cycle whenever the motor 106is energized, a mechanical connection (shown schematically at 110) isprovided between the positioning motor shaft and the start button 76 sothat the variable resistance 108 may be mechanically repositioned to itslowest value each time a new drying cycle is initiated.

The resistances 108 and 54 in the voltage divider circuit areproportioned such that the resistance 108 is much larger, on the orderof 100 to 1, than the sensing element resistance 54. Insofar as thevoltage divider circuit is concerned, therefore, when the motor 106runs, the increase in resistance 108 tends to cancel out or offset aportion of the increased voltage drop across the sensor 54 due to thedrying of the clothes load (resistance 54 increases as the clothesbecome dry). The partial offsetting action tends to delay the point atwhich a ufficient voltage potential exists, base 102 to emitter 88, tofire the transistor 86 and terminate the drying cycle. In effect, thegradually increasing resistance 108 acts to continually decrease thepercent relative humidity requirement of the exhaust air necessary toterminate the drying cycle.

Referring now to FIGURES 1 and 2, the dryer control circuit includessuch normal safety feature as a high limit thermostat 112 which opensupon an abnormal rise in temperature within the heater chamber and amotor switch 114 which is closed by a centrifugally actuated mechanism(not shown) in the main motor 62 to insure that the heater 60 will notbe energized unless the motor 62 is operating to rotate the tumblingdrum 20. In addition to the safety controls, thi circuit includes atermination conrol thermostat 116 responsive to the temperature of airleaving the tumbling drum. The thermostat 116 has a switch blade 118which closes on a heater circuit contact 120 when the temperature of theexhaust air is between and 140 F. or below. Above this predeterminedtemperature range, the switch blade moves to the contact 122 in whichposition it energizes the positioning motor 106 to increase theresistance 108 in the voltage divider circuit. Note that the terminationcontrol thermostat 116 is first moved to its positioning motor contact122 when the sensible temperature of the exhaust air increases suddenlyover the said predetermined temperature range. This generally occurswhen the clothing is reaching a dry condition as reflected by themoisture content of the dryer exhaust air. This dry bulb temperaturejump has been used repeatedly in prior art devices to terminate thedrying cycle. However, such prior art systems fail to cornpensate forthe occasional or LIGHT loads, such as a shag rug or four to five poundof assorted clothing and hardto-dry items wherein fabric seams resistgiving up moisture evenly. in these LIGHT loads, the point at which thesensible temperature jumps above the predetermined temperature range isin advance of the proper dryness end point for the clothes load and,thus, this invention seeks to prolong the cycle by operating the motor106 to gradually reduce the percent relative humidity at which the cyclewill terminate. As has been explained hereinbefore, this is accomplishedby increasing the resistance 108 in the voltage divider circuit to delaythe point at which the humidity sensing element 54 is effective to biastransistor 86 to by-pass the power and shunt the termination relay coil82.

An operating drying cycle will be explained with reference to thecontrol circuit of FIGURE 2 and the graph in FIGURE 3. Note that thegraph in FIGURE 3 takes into account only the last portion of the dryingcycle which shows the manner in which the various type loads terminate.Consider first a NORMAL eight pound load which is placed in the tumblingdrum 20 and the dryer energized by pushing the button 76. At the start,the temperature in the tumbling drum is below 130 F. and the thermostat116 is positioned to energize the heater 6i) and the prime mover or mainmotor 62. The amplifier 56 is actuatable by humidity sensed by thesensing element 54 in the exhaust duct 52. It is possible that thesystem may terminate the NORMAL or regular eight pound load cycle beforethe motor 106 is even ener"izedassuming that the sensor 54 fired thetransistor 86 in advance of the point at which the sensible temperaturejumps to actuate the thermostat 116. In this situation, the NORMALdrying cycle will terminate when the resistance of the element 54 isincreased to the point at which the transistor 86 is biased to shunt thepower from the relay coil 82 to cause the switch 84 to open. However,most loads do ermit the temperature to increase enough to actuate thethermostat 116 and run the positioning motor 106 some. In graphic form,this more usual condition is represented by curve 136 which is showndropping 01f to about to 35% R.H. marl; at which point 138 the relaycoil 82 is deenergized and the cycle terminated before the clothes areoverdried. Thus, at point 138 a NGRMAL eight pound load of clothes i drywhen the resistance of the sensor 54 increases to create a volt-age atthe base 102 which will fire the transistor.

Let us assume now that a LIGHT load, such as a shag rug or a small load(under five pounds) of light fabrics, is being dried. The moisture Willbe very quickly vaporized from the exposed fabric surface in the LIGHTload. However, in the depths of the shag rug and in the folds and seamsof the light fabrics, the moisture will still be retained so that anexhaust air indication of thirty-fivepercent relative humidity would bea premature indication that the load is dry. Consequently, and inaccordance with this invention, when the sensible temperature firstjumps and moves above the predetermined setting of thermostat 116, say140 F., the switch blade 118 will move to the contact 122 to energizethe positioning motor 1116. The motor then starts to gradually increasethe resistance 10% to hold off the point at which the sensing element 54would normally fire the transistor 86 to terminate the drying cycle.This, in effect, lowers the relative humidity setting which is necessaryto terminate the drying cycle.

A load controlled in accordance with this invention would exhibit threecurves of interest. The drying rates of a typical LIGHT load and NORMALload are evidenced on the drying curves 140 and respectively, and therate of depressing termination point relative humidity is shown by thecontrol curve 142. The respective drying cycle will terminate where thedrying curves intersect with the control curves-a variable end pointdepending on the number of times that the thermostat 116 energizes orcycles the control motor 106 while the load is drying. Therefore, themore frequently that thermostat 116 energizes the motor 106 the moreprolonged will be the drying cycle. Thus, it can be seen that the dryingof a NORMAL eight pound load may be terminated at point 138 (35% RH),whereas the drying of the particular LIGHT load evidenced by the curve140 is terminated at point 144 RH). The more gradual the slope of thedrying curve 140 (i.e. the greater the affinity of the load to retainits moisture), the longer will be the total cycle time and the lowerwill be the percent R.H. of the exhaust air when the clothes havereached their proper dryness condition. In short, the positioning motor106 operates solely to adjust the amplifier 56 to terminate the dryingcycle at a lower percent R.H. A detailed description of the improvedamplifier 56 will be described next following. It should be recognized,however, that any conventional amplifier could be substituted for theimproved amplifier within the purview of this invention.

The transistorized humidity element amplifier 56 is used in conjunctionwith the above dryer control. This amplifier has the advantages oftransistor reliability and the novel circuit in which the elements ofthe amplifier are arranged circumvents the disadvantages of transistors,i.e. low input impedance, because the transistor is looking at aconstant input current or high voltage source. In other words, thevoltage across the potentiometer or variable resistance 108 is aconstant 115 voltsa fact which permits a small increase in relativehumidity seen at the sensor 54 to actuate the transistor by a biasingcon nection 102 between the two resistances 108 and 54. The amplifier 56is comprised of the solenoid or relay actuating coil 82 for actuating anormally open switch 84 in the drying cycle start circuit. Whenever thecoil 82 is deenergized, the switch 84 opens to deenergize the coil 78and the drying cycle is thus terminated. For controlling the coil 82,the amplifier 56 further includes the capacitor 94, the diode 92, aresistance 96 small enough to permit energization of the relay coil 82and a transistor 86 having the integral components of collector 90,emitter 88 and the base leg 102.

In operation, the amplifier 56 is connected across the leads L and N ofa 115 volt alternating current power source and functions as follows atthe start of a drying cycle. When the push button 76 is depressed, thepositive half of the AC. sine wave will move from L through the diode92, thereby by-passing the relay coil 82 to the neutral side of theline. On the next half A.C. sine wave, power flow in the negativedirection from N to L will energize the solenoid coil 82 to close theswitch 84. The capacitor 94 is charged and the transistor 86 is inactivedue to low humidity at the element 54. In the next positive half wavefrom L to N, the capacitor 94 discharges to maintain the relay coil 82energized while the diode 92 by-passes the coil. Thus, the coil 82remains energized in one direction by the half wave flow from N to L andin the other direction by the discharge of the capacitor 94. Thissituation maintains throughout the clothes drying cycle since thepredetermined voltage to actuate or fire the transistor 86 is not beingapplied at the biasing leg 102. However, as the cycle progresses,considering the shag rug or LIGHT load characteristic, the resistance108 is increased whenever the motor 106 is energized. At a certainpoint, the voltage applied at 102 through the voltage divider circuitincluding the thermally responsively variable resistance 108 and thehumidity responsive variable resistance 54 will be effective to fire thetransistor 86. When this happens, the capacitor 94 will dischargethrough the transistor 86 instead of the coil 82 and the switch 84 willopen. When switch 84 opens, the holding relay coil 78 is deenergized andswitch 80 opens to terminate the drying cycle.

It should now be seen that an improved clothes dryer termination controlhas been provided wherein a variable end point dryness is effected toaccommodate light loads of light fabrics or loads of heavy deep pilematerial, such as a shag rug. Further, this invention includes a noveltransistorized amplifier wherein the relay coil is placed in parallelwith the transistor and fed from a line voltage source rather than atransformer as in the prior art. This improved amplifier circuitovercomes the problem of matching impedances of the humidity sensingelement and the transistor. It also eliminates the need for a rectifiercircuit since the circuit provides its own DC. power supply.

While the embodiments of the present invention as herein disclosedconstitute preferred forms, it is to be understood that other formsmight be adopted.

What is claimed is as follows:

1. In combination, a clothes dryer having means for conveying a streamof air into moisture absorbing relationship with said clothes in aclothes drying cycle, means for heating said stream of air, controlmeans for energizing or deenergizing said heating means in response tothe temperature of said air, switch means for initiating and terminatingsaid cycle, and voltage divider circuit means for controlling saidswitch means, said circuit means including first resistance means, theresistance of which increases in response to the decreasing relativehumidity of said air as said clothes approach a dry condition forterminating said cycle when a predetermined resistance value is attainedand second resistance means in resistance comparing relationship to saidfirst resistance means, means connected to said second resistance meansand actuatable for increasing the resistance thereof for at leastpartially balancing said first resistance means whenever said controlmeans is deenergizing said heating means, thereby to increase saidpredetermined resistance value and extend said clothes drying cycle.

2. In combination with a clothes dryer having means for conveying astream of air into moisture absorbing contact with said clothes,termination control circuit means comprising a pair of lead wiresconnected across a source of voltage, one of said lead wires including apower termination switch means operable to connect and disconnect saidone of said lead wires from said source of voltage, a first circuitconnected across said lead wires including a relay coil winding, saidpower termination switch means operating to connect and disconnect saidone of said leads from said source of power in response to the actuationof said relay coil winding, a second circuit connected across said leadwires for by-passing said relay coil winding and including asemiconductor switch means, a third circuit connected across said leadwires for by-passing said relay coil winding and said semiconductorswitch means and including first and second resistance elements, andmeans connected to said third circuit between said resistance elementsand associated with said semiconductor switch means for controlling thelay-passing of said relay coil winding, thereby to operate said powertermination switch means, said first resistance element being inhumidity responsive relationship to said stream of air downstream fromsaid clothes, means connected to said sec-0nd resistance element andactuatable for increasing the resistance thereof, and means in thermallyresponsive relationship to said stream of air downstream from saidclothes for actuating said last named means.

3. In combination with a clothes dryer having means for conveying astream of air into moisture absorbing contact with said clothes,termination control circuit comprising a pair of lead Wires connectedacross a source of voltage, one of said lead wires including a powertermination switch means operable to connect and disconnect said one ofsaid lead Wires from said source of voltage, a first circuit connectedacross said lead wires including a relay coil winding, said powertermination switch means operating to connect and disconnect said one ofsaid leads from said source of power in response to the actuation ofsaid relay coil winding, a second circuit connected across said leadwires for by-passing said relay coil winding and including asemiconductor switch means, a third circuit connected across said leadwires for bypassing said relay coil winding and said semiconductorswitch means and including first and second resistance elements, andmeans connected to said third circuit between said resistance elementsand associated with said semiconductor switch means for controlling theby-passing of said relay coil winding, thereby to operate said powertermination switch means, said first resistance element being inhumidity responsive relationship to said stream of air downstream fromsaid clothes, means connected to said second desistance element andactuatable for increasing the resistance thereof, and means in thermallyresponsive relationship to said stream of air downstream from saidclothes for actuating said last named means to increase the resistanceof said second resistance element when the temperature of said stream ofair is above a predetermined value.

4. A drying cycle termination control circuit for a clothes dryer havingmeans for conveying a stream of air into moisture absorbing contact withsaid clothes comprising a pair of lead wires connected across a sourceof Voltage, one of said lead wires including a power termination switchmeans operable to connect and disconnect said one of said lead wiresfrom said source of voltage, a first circuit connected across said leadwires including a relay coil winding, said power termination switchmeans operating to connect and disconnect said one of said leads fromsaid source of power in response to the actuation of said relay coilwinding, amplifier means for selectively actuating said relay coilwinding, a third circuit connected across said lead wires for by-passingsaid relay coil winding and said amplifier means and including rst andsecond resistance elements, and means connected to said third circuitbetween said resistance elements and associated with said amplifiermeans for controlling the bypassing of said relay coil winding, therebyto operate said power termination switch means, said first resistanceelement adapted to be in humidity responsive relationship to said streamof air downstream from said clothes, means connected to said secondresistance element and actuatable for increasing the resistance thereof,and means adapted to be in thermally responsive relationship to saidstream of air downstream from said clothes for actuating said last namedmeans to increase the resistance of said second resistance element,thereby to extend the drying cycle.

5. A drying cycle termination control circuit for a clothes dryer havingmeans for conveying a stream of air into moisture absorbing contact withsaid clothes comprising a pair of lead wires connected across a sourceof voltage, one of said lead wires including a power termination switchmeans operable to connect and disconnect said one of said lead wiresfnom said source of voltage, a first circuit connected across said leadwires including a relay coil winding, said power termination switchmeans operating to connect and disconnect said one of said leads fromsaid source of power in response to the actuation of said relay coilwinding, amplifier means for selectively actuating said relay coilwinding, a third circuit connected across said lead wires for bypassingsaid relay coil Winding and said amplifier means and including first andsecond resistance elements, and means connected to said third circuitbetween said resistance elements and associated with said amplifiermeans for controlling the by-passing of said relay coil winding, therebyto operate said power termination switch means, said first resistanceelement being in humidity responsive relationship to said stream of airdownstream from said clothes, means connected to said second resistanceelement and actuatable for increasing the resistance thereof, and meansin thermally responsive relationship to said stream of air downstreamfrom said clothes for actuating said last named means to increase theresistance of said second resistance element when the temperature ofsaid stream of air is above a predetermined value, thereby to extend thedrying cycle.

6. A power termination control circuit comprising a pair of lead wiresconnected across a source of voltage, one of said lead wires including apower termination switch means operable to connect and disconnect saidone of said lead wires from said source of voltage, a first circuitconnected across said lead wires including a relay coil winding, saidpower termination switch means operating to connect and disconnect saidone of said leads from said source of power in response to the actuationof said relay coil winding, 2. second circuit connected across said leadwires for by-passing said relay coil winding and including asemiconductor switch means, a voltage divider circuit connected acrosssaid lead wires for bypassing said relay coil winding and saidsemiconductor switch means and including first and second resistanceelements, and means connected to said third circuit between saidresistance elements and associated with said semiconductor switch meansfor controlling the by-passing of said relay coil winding, thereby tooperate said power termination switch means; one of said resistanceelements being responsive to a first condition to actuate saidcontrolling means and the other of said resistance elements beingincreasable in resistance to alter the actuation of the controllingmeans by changing said first condition, means connected to said secondresistance element and actuatable for increasing the resistance thereof,and means responsive to a second condition for actuating said last namedmeans.

7. In combination with air impelling means for producing an air streamsubjected to variable conditions of temperature and humidity powertermination control circuit comprising a source of voltage forselectively energizing said air impelling means, a pair of lead wiresconnected across said source of voltage, one of said lead wiresconnectable to said air impelling means and including a powertermination switch means operable to connect and disconnect said one ofsaid lead wires from said source of voltage to energize and deenergizesaid air impelling means, a first circuit connected across said leadwires including a relay coil winding, said power termination switchmeans operating to connect and disconnect said one of said leads fromsaid source of power in response to the actuation of said relay coilwinding, a second circuit connected across said lead wires forby-passing said relay coil winding and including a semiconductor switchmeans, a third circuit connected across said lead wires for by-passingsaid relay coil winding and said semiconductor switch means andincluding a first resistance element in humidity responsive relationshipto said air stream and a second resistance element, means actuatable forprogressively increasing the resistance of said second resistanceelement, means in thermally responsive relationship to said air streamactuating said last named means, and means connected to said thirdcircuit between said resistance elements and associated with saidsemiconductor switch means for controlling the by-passing of said relaycoil winding, thereby to operate said power termination switch means.

8. In combination with air impelling means for producing an air streamand means for subjecting said air stream to variable conditions oftemperature and humidity, power termination control circuit meanscomprising a source of voltage for selectively energizing said airimpelling means and said subjecting means, a pair of lead wiresconnected across said source of voltage, one of said lead wiresconnectable to said air impelling means and said subjecting means andincluding a power termination switch means operable to connect anddisconnect said one of said lead wires from said source of voltage toenergize and deenergize said air impelling means and said subjectingmeans, a first circuit connected across said lead wires including arelay coil winding, said power termination switch means operating toconnect and disconnect said one of said leads from said source of powerin response to the actuation of said relay coil winding, a secondcircuit connected across said lead Wires for bypassing said relay coilwinding and including amplifier means, a third circuit connected acrosssaid lead Wires for by-passing said relay coil winding and saidamplifier means and including a first resistance element in humidityresponsive relationship to said air stream and a second resistanceelement, means for progressively increasing said second resistanceincluding means in thermally responsive relationship to said air stream,said thermally responsive means connected to said one of said lead wiresand having a first position for increasing said second resistance and asecond position for energizing said subjecting means, and meansconnected to said third circuit References Cited by the Examiner UNITEDSTATES PATENTS 2,820,304 1/58 Horecky 3445 2,828,450 3 5 8 Pinckaers.

2,878,580 3/59 Hughes 34-45 2,895,230 7/59 Reiley 3445 2,991,653 7/61Thompson.

3,014,159 12/61 Frank 317--148.5 X 3,032,690 5/62 Elliot 317-148.5 X3,073,244 1/63 Elliot 317148.5 X

NORMAN YUDKOFF, Primary Examiner.

1. IN COMBINATION, A CLOTHES DRYER HAVING MEANS FOR CONVEYING A STREAMOF AIR INTO MOISTURE ABSORBING RELATIONSHIP WITH SAID CLOTHES IN ACLOTHES DRYING CYCLE, MEANS FOR HEATING SAID STREAM OF AIR, CONTROL MEANFOR ENERGIZING OR DEENERGIZING SAID HEATING MEANS IN RESPONSE TO THETEMPERATURE OF SAID AIR, SWITCH MEANS FOR INITIATING AND TERMINATINGSAID CYCLE, AND VOLTAGE DIVIDER CIRCUIT MEANS FOR CONTROLLING SAIDSWITCH MEANS, SAID CIRCUIT MEANS INCLUDING FIRST RESISTANCE MEANS, THERESISTANCE OF WHICH INCREASES IN RESPONSE TO THE DECREASING RELATIVEHUMIDITY OF SAID AIR AS SAID CLOTHES APPROACH A DRY CONDITION FORTERMINATING SAID CYCLE WHEN A PREDETERMINED RESISTANCE VALUE IS ATTAINEDAND SECOND RESISTANCE MEANS IN RESISTANCE